1. Technical Field
Exemplary embodiments of the inventive concept relate to a method of measuring an overlay of an object. More particularly, exemplary embodiments of the inventive concept relate to a method of measuring an overlay of stacked patterns.
2. Discussion of the Related Art
Generally, a plurality of semiconductor fabrication processes is used to form a plurality of lower patterns and upper patterns on a semiconductor substrate. To determine an alignment between an upper pattern and a lower pattern, an overlay between the lower pattern and the upper pattern may be measured.
In an overlay measurement method, the overlay of the lower and upper patterns may be indirectly measured using an alignment mark formed on a scribe lane of the semiconductor substrate. However, the overlay measured in this manner may not accurately represent the overlay of both patterns, since the alignment mark may be off.
In another method, the overlay may be measured using actual images of the lower and upper patterns. This may be more accurate that using the aforementioned alignment mark; however, this method's measurements are obtained after forming the upper pattern. In other words, the actual overlay is measured after a patterning process such as an etching process is performed on an upper layer to form the upper pattern. Therefore, when the overlay measurement indicates that the upper pattern is misaligned with the lower pattern, the upper pattern cannot be realigned, and thus may lead to the disposal of the semiconductor substrate.